Implantable medical devices (IMDs) include devices implantable in a mammalian body that sense medical parameters, monitor medical conditions, administer therapy, or any combination thereof. Typical IMDs include a variety of electrical and/or mechanical components, often including a housing that houses the components. Because the components may be fragile, the housing is usually sufficiently robust to protect the components from forces to which they would otherwise be exposed when implanted within the body. Housings may be constructed from titanium, for example. In order to avoid potentially harmful interactions between the components and bodily fluids, such as corrosion, IMD housings are typically hermetically sealed.
Large components common to most IMDs include a battery, a recharge module or coil, and a hybrid circuit that includes digital circuits, e.g., integrated circuit chips and/or a microprocessor, and analog circuit components. The components, the housing and seal elements each add bulk to the IMD.
In the case of a device having elements that interact with the head, implantation of a bulky IMD presents practical difficulties. In many cases, practical considerations weigh strongly against implantation of a bulky IMD under the scalp and on top of the cranium, and the IMD may have to be implanted at a site remote from the scalp. A typical case involves a sensor or stimulator having leads implanted in the brain. Implantation of the IMD requires several distinct invasive stages, often requiring multiple surgical operations.
For example, implantation of a neurostimulator can include several stages. A first stage entails placement of the leads that deliver stimulation to the brain. The surgeon incises the scalp of the patient and draws the scalp away from the skull. The physician then deploys the leads through burr holes in the skull. In a second state, the physician creates a second incision, such as an incision behind an ear. The surgeon tunnels the leads to the second incision and couples the leads to an extension. The surgeon then tunnels the extension down the neck of the patient, and couples the extension to the neurostimulator. The surgeon then incises the upper chest of the patient, implants the neurostimulator in a sub-clavicular pocket, and closes all of the incisions.
Implantation of an IMD at a remote site can be difficult and time-consuming from the perspective of a surgeon, particularly where the IMD is located a significant distance from the treatment or monitoring site. Moreover, the increased surgical time, increased surgical trauma, and increased amount of implanted material associated with the use of leads and extensions can increase the risk to the patient of complications associated with the implantation of the IMD.